By reconditioning large rolling bearings, rather than replacing them, FAG Industrial Services (FIS) can save customers valuable time and money, while ensuring that the bearing is restored to an acceptable, functionally reliable condition.
As a machine element responsible for transmitting forces, the defect-free functional capabilities of a rolling bearing are a decisive factor in influencing the overall availability of machinery and plant. However, for safety reasons, many rolling bearings are still dismounted and replaced as part of a company's routine maintenance activities, particularly on machinery and plant that is deemed critical.
But what some companies do not realise is that, in many cases, the bearings can be restored to a completely acceptable, functionally reliable condition by using appropriate cleaning and repair techniques.
With its repair service for the reconditioning of large rolling bearings, such as those used in steel and aluminium rolling mills, papermaking machinery, mining and quarrying machinery, mineral processing equipment, the wind energy sector or in shipbuilding, FAG Industrial Services (FIS) can offer customers a significant cost reduction for reconditioned bearings compared to the purchase of new ones.
Save 30 to 85 per cent
Reconditioning or maintenance costs for a large rolling bearing typically amount to between 15 and 70 per cent of the cost of a new bearing, depending on the actual repair or level of maintenance involved. Average costs are around 50 per cent of new purchases, as demonstrated by a recently completed reconditioning contract for a customer in Italy. This work involved the complete overhaul of two large double-row tapered roller bearings from a tunnel-driving machine, each with an outside diameter of 3.4m and a mass of 4.5 tonnes. The total maintenance costs were approximately half of the new purchase price of the two large rolling bearings.
Each planned bearing repair is preceded by an in-depth damage diagnosis that helps to determine whether the repair is worth carrying out and is economically viable for the customer. The costs incurred here – typically between EUR100 and EUR500 – are charged if a repair order then materialises.
In the repair of large rolling bearings, all the negative effects of wear and plastic deformation on the working surfaces are removed. For this work, the FIS Service Centre in Wuppertal, Germany, provides modern production and measurement facilities for the whole of Europe. If certain components cannot be repaired, they are completely replaced. Reconditioning can be applied to all types of rolling bearings, including back-up rollers for Sendzimir roll stands, radial spherical roller bearings with an outside diameter of more than 500mm, cylindrical roller bearings with a bore code of 68 or higher, and tapered roller bearings.
Once the specialists at the Wuppertal repair centre have carried out the appropriate processing, the repaired rolling bearings not only provide the same performance as new bearings, but also, after careful assessment and damage diagnosis, the customer can also, in certain cases, be given the same 24-month warranty as for a new bearing.
When products from other bearing manufacturers are reconditioned, a warranty of 24 months is also applied to all work carried out by the reconditioning centre, but not to the material. For reconditioning of products from other manufacturers, it must always be noted that this is only possible up to repair stage 2; in other words, to repair using polishing. Stage 3 (grinding and replacement of components) and stage 4 (new inner or outer rings) requires consultation with the FIS Service Centre in Wuppertal, since the cost and duration of the repair methods can be considerably different from those for reconditioning of FAG products, especially in the case of spherical roller bearings.
Lead time reduction at Siemens
For many customers, it is not only the lower costs that are attractive; lead times are also crucial. In the case of large bearings, reconditioning frequently offers a significant time saving compared to purchasing new. On average, larger bearings are reconditioned within three months.
However, the reconditioning of large rolling bearings can, in some cases, be carried out even faster than this. In a recent reconditioning contract with the Automation & Drives Division of Siemens AG in Nuremberg, Germany, damage was discovered on a bearing with an outside diameter of 1120mm. The application was on a vertical boring and turning mill for the machining of cast housings for electric motors.
Following telephone discussions between Siemens and engineers at the Wuppertal repair centre, and after checking whether the necessary balls were in stock, a promise of prompt reconditioning was given. The bearing was delivered by the customer to FIS at 6:00pm on the Thursday evening. Just nineteen hours later, the bearing had been inspected, the raceways reconditioned by grinding, new balls had been fitted and the bearing had been packed. About 1:00pm on the Friday, Siemens was able to start shipping the repaired bearing back to site. After a special weekend shift by the Nuremberg maintenance crew at Siemens, production was restarted on the Monday. The costs of production downtime were therefore kept to a minimum.
Tunnel-boring machine bearing repairs
Although the Siemens contract is not a typical example, the Wuppertal repair team works rapidly even in the reconditioning of very large bearings. For example, another recent order was for the repair of the major rolling bearing on a tunnel-boring machine for a USA-based customer.
With a mass of 11 tonnes and an outside diameter of 3275mm, repairing the rolling bearing was a real challenge (the largest size that can currently be machined at the Wuppertal repair centre is 4250mm). After just six weeks, the raceways, which were damaged at several points, had been completely reground by 0.3mm, larger balls (by a margin of 0.6mm) had been fitted and the bearing had been packed ready for return shipping.
In this example, the advantage for the customer was not only the considerable time reduction – the procurement time for a special bearing of this type is generally between six and 18 months – but there was also a significant cost saving too, of around 60 per cent compared to the price of a new bearing.
Reconditioning comprises appropriate cleaning and dismounting of the bearing, the preparation of comprehensive examination reports, including appropriate repair recommendations and reconditioning proposals for various levels of reconditioning. These range from simple polishing repairs, through grinding and replacement of individual components, to the substitution of a complete inner or outer ring. Depending on the specific reconditioning levels required, the relevant predicted costs and the anticipated duration of repair are calculated.
Based on its comprehensive conditioning expertise, the Wuppertal Centre not only offers reconditioning services but also the reworking of bearings. This offers the customer potentially significant savings if existing replacement bearings, for which there is currently no use, converted to fulfil his immediate requirements, rather than purchasing new bearings. These reworking or conversion services may include changing the bearings to have a larger internal clearance and introducing lubrication grooves or holes.
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